1. Field of the Invention
The present invention relates to analyte testing devices, and more particularly, to an alignment system for an optical analyte testing device.
2. Description of Related Art
The need for simple methods to determine the chemical and biological constituents in bodily fluids has increased as point of care testing has gained in popularity. The most common application is the self-monitoring of blood glucose concentrations by patients with diabetes. Diabetic patients frequently administer insulin or take other therapeutic actions based on the test results. As testing is generally recommended multiple times daily and may occur in any setting, an easy to use and relatively inexpensive method to accomplish this task is required. The costs of testing are significant to many diabetic patients, especially elderly patients with fixed incomes and those who are not reimbursed by health insurance plans.
In addition to chronic disease monitoring, there are other applications where simple, low cost testing at the point of care may be desired. For example, many practitioners believe that certain medications could be administered much more effectively, both from a medical outcomes and from a cost perspective, if the circulating level of such medications could be monitored during the course of treatment. Generally, if the level of an analyte or biological agent is important enough, the patient needs to go to a clinic or laboratory and submit to a venipuncture so a test may be run on an expensive clinical instrument. The ability to inexpensively monitor the patient either in the doctor's office or at home could lead to improved outcomes. Given the current pressures on improving the cost effectiveness of health care, inexpensive, easy to use alternatives to expensive test methods would be welcomed.
The National Institutes of Health conducted a large scale study to evaluate the benefit of long term tight control of the blood glucose for the diabetic patient. The study, known as the DCCT, proved that long term tight control of the blood glucose levels in patients had a direct relationship to the health of the patient. One way for the medical profession to monitor the condition of a patient is for the patient to use a blood glucose monitoring system which has a memory unit to record the blood glucose level and other data such as date and time.
Systems for monitoring a patient's condition operate by measuring the concentration of an analyte in a bodily fluid sample derived from the patient. The bodily fluid may include blood, interstitial fluid, or urine. The sample is applied to a portion of a disposable test strip having impregnated therein a reagent selected to react with the particular analyte being tested. The reaction is manifested by a physically detectable change, such as an electrical conductivity increase or a change in an optical property, which is in proportion with the concentration of the analyte in the sample.
The physical change in the test strip is measured using known electrical, electro-optical, electro-chemical or other techniques. The measurement is implemented with appropriate circuitry and/or optics disposed in a meter provided separately from the test strip. The meter engages the test strip such that the physical change caused by the reaction of the analyte with the reagent can be measured by the meter, which then processes the information and generates an indication signal proportional to the concentration of the analyte in the sample.
The alignment of the optical components is important because shifts in the orthogonal coordinates x, y or z result in substantial changes in the reflected light being focused on the detection surface of the photodetector. If the amount of light reflected changed then the results of the test can be compromised. To accomplish the alignment of the components of the prior art meters, an electronic printed circuit board (PCB) is fabricated using precision pick and place equipment which can place the components within 0.0005 inches of true position. The optics block is then located to the component placement by precision holes drilled in the PCB or by a fixture which locates the optics block in relationship to the electronic components. The optics block can assume different configurations which achieve a variety of purposes. One configuration has a series of lenses which transport the light from the LED to the photodetector. A second provides a light piping mechanism similar to fiber optics to transport the light, and a third method creates light tubes which channel the light within the optics block. Any alternate design for the optics light transport system which could be envisioned will work with this method and one skilled in the art could conceive of an alternative means. Lensed optics systems have been used in security systems (i.e. fingerprint recognition) and single uses medical meters but the alignment of the components has required considerable effort to insure proper integration into the test systems.
Many diabetics currently use a test method described in U.S. Pat. No. 5,304,468 to Phillips et al. This system is comprised of an electronic meter and a disposable test strip. The meter reads the color change of the strip, the color change correlating to the concentration of the analyte in the sample applied to the strip. The meter is an expensive and complex instrument which uses multiple light sources or detectors to isolate the reagent color change from the sample color. The user must select the calibration code for the meter to match the calibration code of the test strips. In this way, the meter accommodates a wide range of test strip performance values. The system's optics are large and expensive to manufacture due to the precision alignment requirements of the detector and light source.
U.S. Pat. No. 4,637,403 to Garcia et al. describes an integrated system which provides a method by which the patient lances the finger to get a sample of blood which is then used by the device to read the quantity of analyte in the sample. This system uses a complex optical reflectance system to read the analyte level in the sample.
U.S. Pat. No. 5,279,294 to Anderson et al. describes a hand held shirt pocket device for quantitative measurement of glucose or analytes in biological fluids. The device has a sophisticated electronics system and a sampling system integrated into one device to determine the quantity of analyte in a bodily fluid sample.
U.S. Pat. No. 5,515,170 to Matzinger et al. describes the difficulties of keeping a strip holder and optics system clean and the need to present the test strip in the proper perspective to the optics.
European Patent Specification 0 351 891 B1 to Hill et al. describes an electro-chemical system and electrodes which are suitable for the in vitro determination of blood glucose levels. The system requires the use of expensive electrodes and a sophisticated reader to determine blood glucose levels.
U.S. Pat. No. 4,994,167 to Shults et al. describes a measuring device for determining the presence and amount of a substance in a biological fluid using electro-chemical methods. This system requires a complex instrument and method for the patient to determine the quantitative result.
U.S. Pat. No. 5,580,794 to Allen et al. describes a single use disposable measuring device for determining the presence and amount of a substance in a biological fluid using reflectance methods. This system utilizes an optics and electronics package which are mated in a single plane.
U.S. Pat. No. 5,522,255 to Neel et. al. describes a fluid dose, flow and coagulation sensor for a medical instrument which uses a non-volatile electronic calibration device in the system to check the calibration of the reagent strip.
U.S. Pat. No. 5,053,199 to Keiser et. al. describes an electronically readable information carrier for use with a medical device.
Although many improvements have been made, the cost and complexity of measuring analyte levels in biological samples remains a significant issue for patients and for the health care system. Even patients who are covered for blood glucose monitoring supplies must often purchase the meter and await reimbursement. The need to construct expensive optical systems adds cost and complexity for the manufacturers. The cost of the optics systems is a significant cost of the diagnostic meter and simplifying and reducing this cost factor can have a significant affect on the price to the consumer. The availability of a low cost, simplified quantitative test system for the periodic monitoring of constituents of biological fluids, such as glucose in blood, would make testing more accessible to patients and would improve their well-being and reduce the cost of their care.